A binational effort is underway to find a migrant-rights activist with the local nonprofit Border Angels who went missing while traveling alone through central Mexico.

Hugo Castro’s family and a large network of supporters have asked for the assistance of Mexican law enforcement, the U.S. Consulate and other activist groups in the area to find him. Two prayer vigils were held Saturday in San Diego for his safe return and a third was planned for 3 p.m. Sunday in Chicano Park.

News of his disappearance has gone viral and been shared on social media throughout activist networks in both the U.S. and Mexico.

Castro, a U.S. citizen, is a longtime Border Angels volunteer who heads up the nonprofit’s efforts in Baja California, primarily by delivering food and other donations to the dozens of migrant shelters in the Tijuana area, said the nonprofit’s founder, Enrique Morones. Many of the shelters house an influx of Haitians who have tried to enter the U.S. through Mexico.

Castro left his home in Tijuana April 9 to participate in the Refugee Caravan, with plans to join a large group of people from Central America who are traveling to the U.S. to seek asylum and draw attention to their plight.

Castro’s last contact came Thursday afternoon, when he went live on Facebook in a 20-minute video in which he pleaded for help and for someone to pick him up from the highway between Mexico City and Puebla.

He expressed fear about a group of people following him and said he’d been unable to pay for services with U.S. dollars.

Castro’s partner, Gaba Cortes, was posting updates on the search on her Facebook page and told supporters that the information there is the most reliable source.

“These are difficult times for everyone. … Hugo Castro is still missing and we don't have any substantiated information. We ask you stay tuned for the announcements of the family.”